Intercommunicating system



Sept. 26, 1950 2,523,671

A. W. VINCENT INTERCOMMUNICATING SYSTEM` Filed. Jan. 25, 1949 2 Sheets-Sheet 1 TWISTED TOGETHE/P Filed Jan. 25, 1949 2 Sheets-Sheet 2 "E4 az 51 jIIIIII f7 3a ew 4@ TW/' TOGETHER om 2z I` I I Wa V54@ I si I I I 55a: I fia I I I I Ja I I I I I I I I ff I 7d ,am I if@ 40/ I I I I I n I MK] I I I I 000@ I I I I amr/0N I I I |41@ ml ifm -MI I 4@ 7@ I I ma, [KI I I dm, [l] I I dm, [IQ I -L I I L. J l I J/W/O/v H s/i/o/v 5 @mno/v c ,in f4 IC/If D INVENTOR. @I C HI, C HI I@ "I, I 5 "I, I I@ ,9A/MEW W v//vcf/V DI If 0I If @I If @IIIf fa :a n

Sept 26,' 1950 A. w. VINCENT 2,523,671

INTERCOMMUNICATING SYSTEM 4 HrroR/vfv Patented Sept. 26, 19150 INTERCOMMUNICATING SYSTEM Andrew W. Vincent, Rochester, N. Y., assignor to Talk- Products, Inc., Rochester, N. Y., a corporation of New York Application January 25, 1949, Serial N o. 72,692

8 Claims. l

This invention relates to intercommunicating telephone systems.

In applicants copending application Serial No. 707,867, led November 5, 1946, now Patent No. 2,493,174, d-ated Jan. 3, 1950, there is disclosed an intercommunicating telephone system using a transducer at each station for talking as well as for listening by means ofA an amplier to which the several stations are connected in common.

The present invention has for its purpose the improvement of the intercommunicating system disclosed in the mentioned application whereby selective intercommunication can be effected between two stations of the system; and yet the improved system is simple to manufacture and is easy to install by workmen of limited skill.

A further purpose of the present invention is to provide a selective or non-selective intercommunicating telephone system in which a given station or stations therein can converse with a door station when a doorbell is rung from the last-mentioned station.

The various features and advantages of the system will appear from the detailed description and claims when taken with the drawing in which:

Fig, 1 is a circuit diagram of a selective intercommunicating system having a door answering arrangement incorporated therein; and

Fig. 2 is a circuit diagram of a non-selective intercommunicating system also provided with a door answering arrangement. Figs. 3 and 4 show parts of a modified system.

In the preferred form of the invention, there are provided a plurality of intercommunicating stations A, B, C, station C being provided with the door answering arrangement to be described. These stations are linked in multiple to the input terminal I, the output terminal 2 and the common terminal 3 oi the amplier AMP, by the input wires Ia, Ib, and Ic, as well as by the output wires 2a, 2b, and 2c. and by the common wires 3a, 3b, and 3c. At each of the respective stations, there is located a two-way transducer such as Ta, Tb, and Tc in the form of a moving coil or dynamic loud speaker of the permanent magnet type, the moving coils thereof being designated 4a, 4b, and 4c, respectively. At the several stations there are also provided selectively operable manual switches Sa, Sb, and Sc. Each switch, for example Sa, comprises two manually movable contacts such as 5a and 6a insulated from each other but movable as a unit. These contacts are respectively movable into engagement with two sets of fixed contacts 1a, 8a, and 9a, and Illa, IIa, and I2a. Normally the movable contact 5a automatically returns into engagement with fixed contact 8a while movable contact Iia4 automatically returns into engagement with xed Contact IIa. It will be understood that there is a fixed contact in each set for each station in the system. The switchesl Sb, and Sc, at the remaining stations are identical in construction with the switch just described.

In accordance with the one feature of the invention, at least one of the stations, such as station C, is also provided with an arrangement whereby it can also be connected to a door station to enable conversation to be held with a person who has rung the doorbell at the door station. To this end the station C is also provided with a door switch DS whereby station C can be connected through the amplifier AMP to the transducer Td at the door station.

The moving coil, such as 4a of the transducer Ta has one of its terminals connected to the common conductor 3a while its other terminal is connected to the movable contact 5a of the manual switch Sa. The other moving coils 4b, and 4c, of the transducers Tb, Tc, are similarly connected except that at station C the door switch DS is introduced between the transducer Tc. and the switch Sc.

It will be noted that the input conductor I a is connected in multiple to the Xed contacts la, and 9a but is not connected to xed contact 8a with which the movable contact 5a is normally in engagement. The input conductors Ib, and Ic, are similarly connected at their respective stations B, and C. The output conductor such as 2a is connected to the movable contact 6a at its related station where this contact normally engages the iixed contact IIa. This lastnamed contact has no conductor connected thereto. Output conductors 2b, and 2c, are respectively connected to the movable contacts 6b, and 6c. These contacts respectively normally engage the fixed contacts IIb, I'Ic, these xed contacts likewise having no conductors connected thereto.

The stations A, B, C, are also connected by the linkconductors I3,- I4 and I5, it being understood that a link conductor is provided for each additional station. The link conductor I3 has a branch extending to each station, the branch leading to station A terminates at Contact 8a while the branch leading to station B terminates in contact IIJb and another branch thereof leads to station C where it terminates at contact IIlc.

A branch of link I4 terminates at station A in contact I'Za, While another branch thereof terminates at station B in a contact 8b and a further branch thereof terminates at station C in a contact I2c.

The link I5 has a branch terminating at station A in contact Illa, while another branch thereof terminates in contact I2b at station B and a further branch thereof terminates in contact 8c at station C.

The amplifier AMP is preferably of the multistage capacity-coupled type and uses quick heating vacuum tubes energized from batteries such as are used for the filament supply and plate supply in portable radio receivers. In the preferred form of the invention, the amplifier comprises a pentode tube TI (preferably of the type now known as 1LN5) and also comprises the beam power tube T2 (of the type now known as 3LF4). Each station can selectively connect with any one of the remaining stations. For example, if station A wishes t talk to station B, the switch Sa must be adjusted to position movable contact a into engagement with contact 9a and to position movable contact Ba into engagement with fixed contact I2a which is normally connected to coil 4b of transducer Tb. It will be noted that no circuit is closed at this time to the moving coil 4c of transducer Tc at station C so that this station can not engage in conversation. When manual switch Sa is operated as just described, the coil la of the transducer Ta at station A is connected by the input transformer IS) to the input of the amplifier ANEP while station B is selectively connected to the output off the amplifier by the output transformer 25. The closure of the manual switch Sa at the station A, as just described, completes a direct current circuit for heating the filaments FI and F2 of vacuum tubes TI, and T2. This circuit can be traced from the negative pole of battery BI, conductor I'I, resistor sections I6 and I6', through filaments FI and F2 in series, conductor I8, common conductor 3a, the coil 4a of transducer Ta, movable contact 5a, now in engagement with contact 9a, input conductor Ia, thence through the primary winding of the input transformer I9, to the positive pole of 'battery BI. The plate battery B2 has its negative pole connected to the center tap of filament F2 and through conductor I8 to terminal 3 from which the common conductors 3a, 3b and 3c branch.

Since the tube T2 is of the filament type, changes in plate current cause changes in the filament current because the plate current must enter the filament connections and travel along the filament until the electrons are drawn off into space by the plate. The audio component of the plate current produced across the filamentFZ when the negative terminal of the plate battery is connected to either end of the lament, causes an audio Voltage in the filament circuit which is introduced into the input circuit through the effective series resistance of the shunt capacitor 42 and causes undesirable regeneration or degeneration in the amplifier depending upon which side of the filament the negative battery connection is made. By connecting the negative of the plate battery B2 to the center of the filament F2, the plate current flows out into both halves of this filament before being emitted, thereby producing two audio voltages in the same series circuit which are equal and opposite in direction and therefore cancel with a sufficiently diminished eiTect upon the input circuit as to maintain amplifier stability.

The positive pole of battery B2 is connected by conductor 2U through the resistor 2l to the anode 23 of tube TI and through the primary Winding 24 of the output transformez` 25 to the anode 26 of the tube T2. The screen grid 21 and suppressor grid 28 of tubes TI and T2 respectively are maintained at the proper operating voltage from battery B2 in the well known manner. The input circuit of the tube TI includes the grid 32 of this tube, a volume control unit 32' in the form of a voltage divider connected across the terminals of secondary winding 33 of the input transformer and the condenser 34 connected across the terminals thereof, conductor 35, resistor I6', to the filament FI.

The condenser 3l' couples the output of tube TI to the input circuit of tube T2, which circuit includes the grid 38. A high capacity low voltage capacitor l2 (100 mfd.) is connected across the series connected tube filaments FI and F2 and the resistances I6 and IG so that the talking voltage generated at the speaker station will not appear across the tube filaments, which have a high impedance relative to the speaker voice coil impedance, but will be shunted by the capacitor 42 and will be applied across the low impedance amplifier input.

The low impedance secondary Winding 29 of the output transformer has'its terminal 30 connected to the common terminal 3 and has its terminal 3l connected to the output terminal 2. The common terminal 3 and the output terminal 2 are connected in a circuit including the transducer coil ab at the station B which was selected by the party at station A when he adjusted the switch Sa in the manner already described. This circuit may be traced from terminal 3, conductor 3b, transducer coil b, link I4, contact IZa, movable contact 6a, conductor 2a to terminal 2.

When the person at station B is to reply to station A, the switch Sa is released whereby its movable contact 5a engages fixed contact 8a leading to conductor I 3, and its movable contact 6a engages the blank contact IIa. These operations disconnect station A from the input of the amplifier and reconnect that station to the link conductor I3. The switch Sb at station B is moved to the left so that movable contact 5b engages contact 'Ib and movable contact 6b engages Ilib. In this way station B is connected to the input of the amplifier and station A is connected through link conductor I3 and movable contact Gb, to the output of the amplifier. By the alternate operations of the switch Sa and Sb, the parties at the stations A and B can alternately talk and listen.

In the event that station A desires to talk to station C, switch Sa is now moved to the left to connect the transducer Ta to the input of the amplifier. Station C is connected to the output of the amplifier in the same manner as when station B was called since switch DS is now in the position illustrated.

In the event that the doorbell (not shown) is rung from the door station, the person at station C can talk with the party who rang the doorbell. This is effected by moving the movable contact 40 of switch DS to the right until it engages the Contact il which is connected to the conductor Ic. This connects the transducer Tc at station C to the input of the amplifier. Also when switch DS is moved to the right the Vmovable contact 42' of this switch engages Contact 43 which is con'- to one end of the transducer coil 4d, the other end of which is connected by conductor 3d to thev common terminal 3 of the ampliiier. lThus the transducer Td is connected across the output oi the amplier. Station C 'can now talk to the party at the door station. vWhen station C desires to listen to the party at the 'door station, the switch DS is moved to the left, to bring the movable contacts l and i2 into enga-gement with the contacts 45 and 45 respectively. This operation connects the transducer. Td to the input of the amplied and the transducer Tc to the output of the amplier.

It will be noted that the input conductors of an originating station (which, of course, can be any of the stations) as well as the output conductors thereof extend to the station and back to the amplifier through two closed loops, the speaker lead being in series with the input` loop. Since the output circuit or loop is oi higher power than the input circuit or loop, inductive ,coupling is set up to the input loop with the resultant feedback action. In the circuit diagram of Fig. 1, the input circuit of calling station A is drawn in much heavier lines than the remainder of the diagram and the output circuit is drawn in slightly heavier lines since it is assumed that the telephone connection is being made from station A to station B. From this it will be seen that there are two current loops in the originating station A and a single current loop at the called station B. It will be appreciated that the two loops in the calling station tend to cause feed-back diiiculty. In order to avoid this difficulty, coupling must be reduced to a low degree by separating into groups the triple wires of each of the tW-o mentioned loops and then twisting together the wires of a group. In this grouping the common wire, the speaker wire and the input wire are in one group and the output wire and link wiresare'arranged in another group. By this arrangement, the stations such as A, B, and C, can be located as far as five hundred feet from theramplier with the insulation of the wires of the two twisted groups touching each other. If it is desired to have the amplier at a distance greater than five hundred feet from the stations, the groups-of twisted wires are separated a distance apart. It should be pointed out that the common circuit must be extended individually to the common terminal 3 of the amplifier since input and output current is `carried by each common conductor. Also it is necessary to bring all leads or conductors backto a common point near the amplifier since the elimination of an output lead or an input lead inthe twisted groups would destroy the balance.

The doorbell answering arrangement just described can also be incorporated in a non-selective intercommunicating telephone system as disclosed in Fig. 2. In this form of the invention, the amplifier' is arranged in the same manner as that shown in Fig. 1 but differs therefrom in that it has a divided output represented by the output terminals 2 and 2 for the purpose of neutralizing capacitive coupling as will be described; Terminal 2 is connected by conductor 5@ tothe terminal 30 of the output transformer winding 29 while output terminal 2 is connected iby the conductor 52 to the terminal 3l of the output transformer winding 29. The intermediate point 5| of winding 29 is connected by conductor 53 tov the common terminal 3 of the amplifier. Except for these mentioned differences, corresponding elements of the amplifiers shown in Figs 1 and 2 are designated by the same reference characters.

. It will be noted that the selective link conductors I3, I4 and I5 of the system of Figi. 1 are not necessary in the non-selective system shown in Fig. 2 and have, therefore, been omitted.

The stations A, B, and C in the non-selective system are provided with switches Sa', Sb and Sc respectively. Each of these switches includes an output or listen contact such as 53a and an input or talk contact such as 54a as well as a movable contact 55a which normally returns into engagement with Contact 53a for listening, when released, but can be moved to engage contact 51m)` when the party at station A wishes to talk. Sta-Y tion C, whi-ch is equipped with the door answering arrangement, is provided with a door switch DS. The construction and operation of this door switch is'simliar to that of door switch DS in the selective system of Fig. 1.

In the system disclosed in Fig. 2, when a station such as station A desires to talk with the stations B and C the switch Sa' is held at the talk position. This advances the switch blade 55a into engagement with the contact 54a. Station A is now connected to the input of the amplifier while stations B and C are connected to the output thereof so that the person at that station A can talk with a person at the distant stations B or C or with persons at stations B and C when the person at a distant station holds the switch thereat in the talk position while the person at station A releases his switch to the listen position, the person at the distant station can reply. By proper manipulation of the switches at the respective stations, intercommunications can be effected between them. Y

In the event that the doorbell (not shown) is rung from the door station, it will be heard at station C. The person at station C will operate to the right, the door switch DS at-his station. This will simultaneously swing switch blade 5l into engagement with the input contact 53 of the amplifier and switch blade 59 into engagement with the output contact 6l) of the amplifier. The

I person at station C can now talk with the party at the door station. When the person at station C wishes a reply from that party the door switch DS' is operated toward the left. This brings the switch blade 51 into engagement with the amplier output contact 6I and the switch blade 59 into engagement with the amplier input contact 62. Station C can now listen to the party at the door station. By proper manipulation of the door switch DS intercommunication between station C and the door station can be carried on.

It will be noted that wires 2a and 2b are connected to the output terminal 2 of the amplifier vwhile conductor 2c is connected to the amplifier output terminal 2 to effect electrical balance at the amplifier necessitated by the different lengths of these wires. For example, if wire 2c is four hundred feet long, it can be balanced by the combined lengths of wires 2a and 2b, each of which is assumed to be two hundred feet long. Y

The system disclosed in Fig. 1 is arranged for communication between three stations A, B, and C. If the system is enlarged to effect communication between iive stations A, B, C, D and E the switching .means at each station will be duplicated in the manner indicated in Fig. 3. Also a link will be provided for each station that is added. The link of each station such aslink I3 of station A is connected to contact 8 of its related switch while this link terminates at the contacts A at each of the four other stations in accordance with the pattern indicated in Fig. 4.

vThe remaining links for stations B, C, D and E will be connected in a similar manner and will terminate at the contacts designated by their respective station letters at each of the other stations as indicated in Fig. 4.

In operating this enlarged system, the party originating a call, will select the upper or lower of his switching units through which a `Wanted station can be reached. The selected switching unit is then operated to the right or left as the case may be to effect a connection to a wanted station through the link thereof.

It will be understood that the system can be further enlarged by the provision of additional switching units at each of the stations and by the provision of a link for each station added. The connection of the several links will be similar to that indicated in Fig. 4.

What I claim is:

1. In an intercommunicating telephone system, a plurality of stations, a link individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplier common to said stations, selectively operable switching means at each station comprising primary and secondary sets of inactive contacts and a primary active contact cooperating with said primary set and a secondary active contact cooperating with said secondary set, each active contact being movable into engagement with the inactive contacts of its set, the primary active contact at each station being normally in engagement with one of its inactive A contacts at its station, said amplier being provided with an input terminal, an output terminal and a common terminal, means connecting the primary active contact at each station in series with the transducer at its station to said common terminal, means for connecting a plurality of the remainder of said primary inactive contacts at each station being connected to said input terminal, a branch of the link conductor individual to a given station terminating in the primary inactive contact with which its primary active contact is normally in engagement at said given station, means connecting the secondary active contact at the given station to said output terminal, a branch of each of the remaining links terminating in an individual inactive secondary contact at the given station.

2, In an intercommunicating telephone system, a plurality of stations, a link individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplier common to said stations, selectively operable switching means at each station comprising primary and secondary sets of inactive contacts and a primary active contact cooperating with said primary set and a secondary active contact cooperating with said secondary set, each active contact being movable into engagement with the inactive contacts of its set, the primary active contact at each station being normally in engagement with one of its inactive contacts at its station, said Iamplier being provided With an input terminal, an output terminal and a common terminal, means for connecting the primary active contact at each station in series with the transducer at its station to said common terminal, means for connecting a plurality of the remainder of said primary inactive contacts at each station to said input terminal, a branch of the link conductor individual to a given station terminating in the primary inactive contact with Iwhich said primary active contact is normally in engagement at said given station, means for connecting active contact at the given station to said output terminal, a branch of a link individual to a given station terminating in a secondary inactive contact at each of the remaining stations, said last-mentioned inactive contacts being arranged in different permutations with respect to their respective cooperating secondary active contacts.

13. In an intercommunicating telephone system, a plurality of stations, a link individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplifier common to said stations, selectively operable switching means at each station cornprising primary and secondary sets of inactive contacts and a primary active contact cooperating with said primary set and a, secondary active contact cooperating with said secondary set, each active contact being movable into engagement with the inactive contacts of its set, means for simultaneously moving the primary and secondary active contacts at each station, the primary active Contact at each station being normally in engagement with one of its inactive contacts at its station, said ampliiier being provided With an input terminal, an output terminal and a common terminal, means for connecting the primary active contact at each station in series with the transducer at its station to said common terminal, means for connecting a plurality of the remainder of said primary inactive contacts at each station to said input terminal, a branch of the link conductor individual to a given station terminating in the primary inactive contact with which said primary active contact is normally in engagement at said given station, means for connecting the secondary active contact at the given station to said output terminal, a branch of each of the remaining links terminating in an individual inactive secondary contact at the given station.

4. In an intercommunicating telephone system, a plurality of stations, a link individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplifier common to said stations, selectively operable switching means at each station comprising duplicate primary and duplicate secondary sets of inactive contacts and a primary active contact cooperating with each set of said primary inactive contacts and a secondary active contact cooperating with each set of said secondary inactive contacts, each active contact being movable into engagement with inactive contacts of its set, the primary active contacts at each station being normally in engagement with one of their inactive contacts at their station, said amplier being provided with an input terminal, an output terminal and a common terminal, means for normally connecting the primary active contacts at each station in series With the transducer at their station to said common terminal, means for connecting a plurality of the remainder of said primary inactive contacts at each station to said input terminal, means for connecting the link conductor individual to a given station to the primary inactive contacts with which said primary active contacts are normally inlengagement at said given station, means for connecting the secondaryfactive Vcontacts; "at the given station to said output terminal, a branch of each of the remaining links terminating in an individual inactive secondary contact at the given station, said branches at the several stations terminating in said secondary inactive contacts in accordance with diiierent permutations whereby selective telephone interconnections of said stations can be effected',

5. In an intercommunicating telephone system, a plurality of stations, a link individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplifier common to said stations, selectively operable switching means at each station oomprising primary and secondary sets of inactive contacts and a primary active contact cooperating with said primary set and a secondary active contact cooperating with said secondary set, each active contact being movable into engagement with the inactive contacts of its set, the primary active contact at each station being normally in engagement with one of its inactive contacts at its station, said amplifier being provided with an input terminal, an output terminal and a common terminal, means for connecting the primary active contact at each station in series with the transducer at its station to -said common terminal, means for connecting a plurality of the remainder of said primary inactive contacts at each station to said input terminal, the link conductor individual to a given station terminating in the primary inactive contact with of said stations for connecting the transducer.

thereat to the input portion of the ampliiier and the substation transducer to the output portion Y of the amplifier and vice versa whereby conversation can be conducted through the last-mentioned transducers.

6. In an intercommunicating telephone system, a plurality of stations, aV link conductor individual to each station and having branches terminating at the remaining stations, a transducer at each station serving both as a microphone and as a receiver, an amplier common to said stations, selectively operable switching means at each station comprising primary and secondary sets of inactive contacts and a primary active contact cooperating with said primary set and a secondary active contact cooperating with said secondary set, each active Contact being selectively movable into engagement with the inactive contacts lof its set, the primary active contact at each station being nortacts at its station, such amplier being provided with an input terminal, an output terminal and a common terminal, means including a conductor connecting the primary active contact at each station in series with the transducer at its station to said common terminal, an inputv conductor connecting a plurality of the remainder of said primary inactive contacts at each station to said input terminal, the link conductor individual to a given station terminating in the primary inactive contact with which said primary active contact is normally in engagement at said given station, an output conductor connecting the secondary active contact at the given station to said output terminal, said lastmentioned inactive contacts at the several stations being arranged in different permutations with respect to their respective cooperating secondary active contacts, and means for reducing electrical coupling between a, group of said electrical conductors including an input conductor and a group of conductors including an output conductor.

'7. In an intercommunicating telephone system, a plurality of stations each provided with a transducer for transmitting and for receiving signals, an electronic audio ampliiier having an input portion and an output portion, each station having an input conductor coupled to the input portion of the amplifier as well as an output conductor coupled to the output portion of said amplifier and a common conductor connected to said amplifier, means including a manual switch at each station normally connecting the transducer thereat in circuit with the output conductor and with the common conductor thereof in readiness for the reception of signals from said amplifier, the switch at each station being operable at will to connect the transducer thereat in circuit with the input conductor and with y the common conductor thereof for the transmission of signals from the station to each of the other stations while the switch is operated, a substation including a transducer located at a remote point, and means including supplemental switching means at one of said stations for connecting the transducer thereat to the input portion of the ampliiier and the substation transducer to the output portion of the amplifier and vice versa whereby conversation can be conducted through the last-mentioned transducers.

8. In an intercommunicating telephone system, a plurality of stations each provided with a transducer for transmitting and receiving signals, an audio ampliiier having an input portion and an output portion, said amplifier including at least one electron tube provided with a iilamentary cathode, a source of direct current, each station having an input conductor coupled to the input portion of the ampliiier as well as an output conductor coupled to the output portion of said amplifier and a common conductor connected to said amplifier, means including a manual switch at each station normally connecting the transducer thereat in circuit with the output conductor and with the common conductor thereof in readiness for the reception of signals from said ampliiier, the switch at each station being operable at will to connect the transducer thereat in circuit with the input conductor and with the common conductor thereof for the transmission of signals from the station with the operated switch, a circuit completed by said last-mentioned switch and including in series said cathode, said source of direct current together with said last-mentioned input and common conductors, a substation including a transducer located at a remote point, and means including supplemental switching means at one of said stations for connecting the transducer thereat to the input portion of the ampiier and the substation transducer to the output portion of the amplier and vice versa whereby conversation can be conducted through the last-mentioned transducers.

ANDREW W. VINCENT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Certificate of Correction Patent No. 2,523,671 September 26, 1950 ANDREW W. VINCENT It is hereby certified that error appears in the printed specification of numbered patent requiring correction as follows:

Column 8, line 11, after the Word connecting line 2, for such read said; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oiice.

Signed and sealed this 28th day of November, A. D. 1950.

the above insert the secondary; column 10,

THOMAS F. MURPHY,

Assistant Gommsszouer of Patents. 

